The invention comprises improvements in an automatic transmission control system of the kind shown in U.S. Pat. Nos. 5,612,874; 5,586,029; and 5,642,283. Each of these prior art patents is assigned to the assignee of the present invention. Their disclosures are incorporated in this disclosure by reference.
The present invention includes features that are common to each of the prior art patents identified above. The '874 patent describes an automatic upshift and downshift control for a four-speed ratio version of the transmission gearing of the present invention. The control includes a pressure build-up system with one variable force solenoid. The electronic control pressure that responds to control strategy executed by an electronic microprocessor is distributed to a booster valve in the main regulator valve system. The main regulator valve effects control of the brake capacity and clutch capacity for all operating conditions. The regulator valve system can be calibrated to provide appropriate pressure needed for achieving the smooth ratio changes without affecting the control strategy required to maintain clutch and brake capacity under stall conditions. Conventional accumulators are not required to soften the engagement of the clutch and the brakes since the pressure boost system is capable of adjusting the capacity of the main regulator valve to achieve optimum upshift and downshift smoothness. A separate valve system is used for forward drive engagements and for reverse drive engagements.
The '029 patent describes a transmission having a compound multiple ratio gear set in combination with a simple planetary gear set as in the case of the present invention. A first overrunning coupling establishes a reaction element for the simple planetary gear set and a second overrunning coupling in the multiple ratio gear set is used for the purpose of establishing non-synchronous shifts in the multiple ratio gear set. In each instance, a forward engagement is obtained by engaging a forward clutch. A separate reverse engagement clutch is used to establish a torque flow path for reverse. In each instance, turbine speed is used as a feedback signal to initiate the start of either the forward engagement or the reverse engagement.
The '283 patent, like the '874 and the '029 patents, has a three-speed ratio gear set in series with a simple planetary gear set. It provides five forward driving ratios, however, rather than four. So-called "swap-shifts" are achieved as the multiple ratio gear set is upshifted and the simple planetary gear set is downshifted. Conversely, an upshift of the simple planetary gear set occurs as the multiple ratio gear set is downshifted. The torque reaction point for the overall transmission gearing is transferred from the multiple ratio gear set to the simple planetary gear set on a downshift and is transferred from the simple planetary gear set to the multiple ratio gear set on an upshift.